noun

• (uncountable) The supreme effort one can make, or has made.
  "I did my best."
• (uncountable) One's best behavior.
  "I was somewhat distant lately, and my lady promised me head every Tuesday of the week when I’m nice to her, so I better be on my best."
• (countable) The person (or persons; or thing or things) that is (are) most excellent.
  "Even the best of us makes mistakes, but only a few with the best of intentions..."

verb

• (transitive) To surpass in skill or achievement.
• (transitive) To beat in a contest.
  "The Norddeutscher Lloyd steamship Kronprinz Wilhelm left New York on May 3 [1904], at 3.10 p.m. and reached Plymouth Sound on May 9 at 8 a.m. This was then a very fast crossing of the Atlantic, but it was not the record. The same ship had held the "Blue Riband" in 1902, but had been slightly bested by the Kaiser Wilhelm II, a larger vessel of the same line, in 1903, and that stood as the record until the Cunard Line secured the honours in 1909 with the Mauretania and held them for an unbroken period of 20 years."

verb

• (modal, colloquial) Had best.
  "It's getting late. You best get on home."